Ultrahigh Conductivity and Superior Interfacial Adhesion of a Nanostructured, Photonic-Sintered Copper Membrane for Printed Flexible Hybrid Electronics

Abstract

Inkjet-printed electronics using metal particles typically lack electrical conductivity and interfacial adhesion with an underlying substrate. To address the inherent issues of printed materials, this Research Article introduces advanced materials and processing methodologies. Enhanced adhesion of the inkjet-printed copper (Cu) on a flexible polyimide film is achieved by using a new surface modification technique, a nanostructured self-assembled monolayer (SAM) of (3-mercaptopropyl)trimethoxysilane. A standardized adhesion test reveals the superior adhesion strength (1192.27 N/m) of printed Cu on the polymer film, while maintaining extreme mechanical flexibility proven by 100 000 bending cycles. In addition to the increased adhesion, the nanostructured SAM treatment on printed Cu prevents formation of native oxide layers. The combination of the newly synthesized Cu ink and associated sintering technique with an intense pulsed ultraviolet and visible light absorption enables ultrahigh conductivity of printed Cu (2.3 × 10 −6 Ω•cm), which is the highest electrical conductivity reported to date. The comprehensive materials engineering technologies offer highly reliable printing of Cu patterns for immediate use in wearable flexible hybrid electronics. In vivo demonstration of printed, skin-conformal Cu electrodes indicates a very low skin-electrode impedance (<50 kΩ) without a conductive gel and successfully measures three types of biopotentials, including electrocardiograms, electromyograms, and electrooculograms.

Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment

“…To use hydrophilic nanomaterial as a pillar, the substrates should be treated beforehand to increase the number of hydrophilic functional groups on their surface and this may lead to outer water penetration. [241,242] Also, the surface charges and hydrophobic property of all the components, such as sensing materials, layouts, and membranes, should be considered in providing the WFHE hybrid functionalities. Specifically, several different areas have deeply discussed such hydrophilic-hydrophobic nature: 1) microfluidic channels, 2) adhesions, 3) newly emerging materials including ionic conductors, and 4) immobilization of biosensors.…”

“…Kwon et al recently reported a Cu electrode with a high conductivity of 43 478 000 S m −1 via inkjet printing followed by an intense pulsed light sintering method. [242] These low-cost and highly conductive electrode arrays were mounted on a soft membrane with a PI encapsulation layer, enabling the detection of physiological signals such as electrooculogram (EOG), EMG, and ECG. Currently, an LM is of great interest in terms of its intrinsic liquid-like feature and thus high conductivity over high strain combined with the scalable printing processes.…”

Surface and Interface Designs in Copper-Based Conductive Inks for Printed/Flexible Electronics

“…Besides, silane coupling agents also tend to make the Cu electrode brittle and fragile. To address this matter, Kwon et al employed surface modifications with a self-assembled monolayer (SAM) of (3-mercaptopropyl) trimethoxysilane on the oxygen-treated PI film to enhance the adhesion of the inkjet-printed Cu electrode from a Cu complex ion ink on PI film [ 156 ] ( Figure 21 c). The superior adhesion strength (1192.27 N/m) and the excellent mechanical stability on 100,000 bending cycles were demonstrated on the printed Cu films on the PI substrate.…”

“…( d ) Recorded biopotentials by the skin-mounted electrodes, including electrophysiological monitoring of electromyograms(EMG), with three gestures. Reprinted with permission from reference [ 156 ], Copyright American Chemical Society, 2018.…”

Inkjet Printing Controllable Polydopamine Nanoparticle Line Array for Transparent and Flexible Touch‐Sensing Application

“…[1][2][3][4][5][6][7][8] Among these fabrication techniques, drop-on-demand inkjet printing using functional material inks has received considerable attention. Inkjet printing presents a promising approach toward the realization of cost-effective, environmental-friendly, and scalable printed electronics, [9,10] and thus holds significant potential for flexible, [11,12] stretchable, [13,14] and hybrid [15,16] electronics applications. However, a major limitation of inkjet printing is low resolution (typical feature size ranges from 35 to 100 μm), [17,18] which hinders further development of this technique for advanced microelectronics applications.…”